1. Field of the Invention
The present invention relates to a technique for sensing whether or not there is abnormality in a pressure sensor used for pressure control of a liquid discharge device typified by an ink jet device.
2. Description of the Related Art
In ink jet equipment, in order to normally eject ink from a nozzle of a print head, it is essential to perform appropriate back pressure control. Particularly, to perform appropriate back pressure control, it is indispensable that a pressure sensor of the control system output a correct pressure value.
However, there is a case where a failure occurs at a pressure sensor provided on an ink channel due to chemical wear or the like caused by ink, and the pressure sensor outputs a value different from an accurate pressure value. In such a case, normal back pressure control cannot be guaranteed, which causes abnormality in an ejection environment and eventually results in degradation in quality (image abnormality) of a printed image.
As a simple method for sensing abnormality of the pressure sensor, there is a method in which a sensor for calibration (for example, a pressure sensor corresponding to an additional one set) is separately provided. However, because such a method increases cost of the equipment, a configuration is desirable in which abnormality can be sensed using the pressure sensor alone.
Japanese Patent Application Laid-Open No. 2012-183806 (PTL 1), Japanese Patent Application Laid-Open No. 2000-229422 (PTL 2) and Japanese Patent Application Laid-Open No. 2012-016904 (PTL 3) refer to abnormality sensing within an ink channel or an ink circulation control method. PTL 1 discloses sensing abnormality within the channel by determining whether or not an ink circulation amount acquired from speed of a pump is a normal value. PTL 2 discloses sensing abnormality of an ink channel by recognizing relationship between an appropriate value of an ink pressure and a number of rotation of a motor which drives a pump in advance and determining whether or not the number of rotation of the motor falls within a fixed allowable range. PTL 3 discloses providing differential pressure adjusting means for detecting pump speed and securing an appropriate circulation amount.